Passage Summary: Ancient kangaroos were built for climbing trees, but today's tree-climbing kangaroos lack the specialized thumbs and tails their ancestors had, even though those tools would be very useful.

Reasoning: The ancestors of all kangaroos had traits for climbing trees, and while it makes sense that land-dwelling kangaroos lost them, it is strange that modern tree-dwelling kangaroos also lack them.

Analysis: The paradox here is an evolutionary 'missing link'—why would a creature living in the trees lack the very traits its ancestors had that were perfectly suited for that environment? We need a piece of information that explains why modern tree-dwelling kangaroos wouldn't have these attributes despite their utility. A likely resolution would involve the lineage of these animals; perhaps modern tree-dwellers evolved from land-dwellers who had already lost those traits, rather than descending directly from the original tree-dwelling ancestors. Look for an answer that explains this 're-evolution' or provides a reason why those specific traits are no longer necessary.